1. Field of the Invention
The present invention relates to a device for use in scanning type electron microscope and adapted for shifting frozen specimen.
2. Description of the Prior Art
It is a commonly adopted measure to observe a specimen by a scanning type electron microscope, in a frozen state of the specimen. This method of observation is advantageous because the observation can be made without deterioration and distortion of the specimen. For this reason, the technique for observing frozen specimen is becoming important.
According to a prior art technique, the biological specimen is held by a specimen holder and is immersed, together with the holder, in a refrigerant (liquefied nitrogen) stored in a refrigerant vessel, under atmospheric pressure, so as to be frozen instantaneously. Then, the frozen specimen is covered, and is taken out to the atmosphere together with the specimen holder. The frozen specimen is then shifted to a preparation chamber which communicates, through an air lock valve, with an evacuated specimen chamber, and is placed on a specimen table disposed in the preparation chamber. The preparation chamber is evacuated to a predetermined level of vacuum. Then, the cover is opened by making use of an operation instrument operable from the outside of the preparation chamber and, after opening of the air lock valve, the specimen is shifted, together with the specimen holder and the cover, to a specimen table disposed in the specimen chamber. The electron microscope is operated in this state, for the observation of the specimen.
This prior art technique involves various problems. Namely, it is necessary to provide means for opening the cover in the preparation chamber. This inevitably leads to a complicated construction of the preparation chamber. At the same time, since the shifting of the specimen from one to the other of the preparation chamber and the specimen chamber is made with the cover in the opened state, the shifting is considerably obstructed by the opened cover.
In many cases, it is necessary to effect a certain treatment such as scratching by a knife or an ion spattering on the frozen specimen in the preparation chamber. In order to prevent the specimen from being frozen and deteriorated or distorted during this treatment, it is necessary to provide means for maintaining the specimen table in the preparation chamber at a sufficiently low temperature. At the same time, for preventing the specimen from being molten and deteriorated or distorted during the observation, it is necessary to provide means for cooling the specimen table in the specimen chamber down to an adequate low temperature. Thus, the described prior art technique necessitates two independent cooling means, resulting in a complicated construction around the specimen chamber and increased rate of consumption of the refrigerant for the cooling of the tables.